Indicating fuse with protective shield

ABSTRACT

A pin indicating fuse construction incorporates a protective shield member that isolates an indicator assembly from a main-fuse link. By use of the inventive protective shield, arc-quenching filler may be excluded, resulting in a less-costly, more reliable fuse construction. The main fuse link is arranged within the fuse in such a manner so as to minimize potential interference with the actuator assembly during activation of the indicator assembly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to fuses generally, and in particular it relatesto fuses incorporating an indicating device.

2. Related Art

Fuses incorporating indicating devices are generally known in the art.An existing indicating fuse design 100 is illustrated in FIG. 3A. A fusebody 116 optionally includes an orientation ring 114 that may bedisposed on the periphery of the fuse body 116. The orientation ring 114serves to insure proper installation of the fuse 100. The precisestructure and function of such an orientation device is described inU.S. Pat. No. 5,549,404, the disclosure of which is incorporated hereinby reference.

Terminals 118 and 120 are disposed at opposite ends of the fuse. A mainfuse element or link 122 is electrically connected to each of theterminals 118, 120. The majority of current passing through the fuse 100is carried by the main fuse element 122 during normal operatingconditions. "Normal operating conditions", or the normal operative stateof the fuse is intended to mean a condition wherein the main fuseelement 122 is intact, and current can pass from one terminal (118 or120), through the fuse 100 without substantial interruption, and out ofthe fuse through the opposite terminal (118 or 120).

A conductor wire 142 is connected at one end to one terminal 118, and toan end of an indicator assembly 144. The indicator assembly includes anindicator pin 146, having a flat or "planished" end 148, a biasingmember sleeve 156, and a biasing member 158 that contacts the bottom ofthe sleeve 156 and the head of the indicator pin 146 thereby tending tourge the indicator pin outward. The conductor wire 142 is attached tothe planished end 148 of the indicator pin 146 thereby preventing theindicator pin 146 from being urged outwardly from the fuse by biasmember 158 during normal operating conditions.

The fuse 100 normally includes a granular arc-quenching medium 150 inorder to suppress and contain arcing during destruction of the main fuselink when the fuse 100 is "blown". The arc-quenching medium is typicallya fine granular substance such as sand, terra alba, or mixtures thereof.

In certain lower amperage rated ruses, conductive wire 142 also servesas the main fuse link, thereby enabling omission of a separate main fuselink element 122 from the fuse 100 construction.

During normal operating conditions current is carried through the fuseprimarily via main fuse link 122. In the event that the main fuse link122 is destroyed (e.g., during an overload condition), current isdiverted to the conductor wire 142. The capacity of conductor wire 142to carry current is substantially less than that of main fuse link 122.Therefore, upon the above-mentioned diversion of current, conductor wire142 is quickly destroyed. The conductor wire 142 is no longer capable ofrestraining the indicator pin 146, so bias member 158 urges the pin 146outward from the fuse body 116 thereby indicating a blown fuse condition112.

Various problems are associated with existing fuse constructions.

Historically, pin-indicator fuses generally require an arc-quenchingfiller in order to provide adequate performance for fuses rated atapproximately 5 Amps or greater. This is particularly true for fuseshaving a current rating in excess of 15 Amps. However, inclusion of sucha filler adds to the manufacturing costs of the fuse. Clearly, thefiller adds to the materials cost of the fuse. Also, granular fillersare very destructive to the manufacturing equipment that is used tostore, transport, and introduce the filler into the fuse. The filleralso tends to adversely impact operation of the fuse indicator assemblyby fouling the spring biasing element and otherwise inhibiting propermovement of the indicator assembly components. Moreover, the heat andelectrical arcing associated with destruction of the fuse link can causea reaction with the filler and produce aggregates or globules of fillerwhich further act to prevent proper activation of the indicator assemblyand movement of the indicator pin.

Another problem associated with existing designs is that the main fuselink may be deformed when the fuse is "blown" so that it comes intocontact with the indicator pin thereby preventing the indicator pin frombeing pushed outwardly away from the fuse body to clearly indicate thefuse has been "blown".

A related problem is that the main fuse link can at least partially meltupon destruction and become affixed or welded to the conductor wirethereby preventing the indicator pin from properly emerging from thefuse.

Yet another problem associated with the existing designs is that gasesproduced during destruction of the fuse link can escape the fuse throughthe hole that the indicator pin passes through.

U.S. Pat. No. 4,023,133 to Knapp, Jr. discloses an indicating fusehaving a fuse body containing an arc-quenching filler. A main fuseelement connects two terminals. A wire is connected to one terminal andto a pin so as to restrain the pin during normal operation. When thewire melts, or is otherwise destroyed, the pin is urged outwardly andactivates a complicated indicator assembly. A cap is provided whichsurrounds the biased pin actuator. As noted above, the inclusion of agranular filler adds to the cost of the fuse and may adversely affectthe operation of the fuse. The indicator assembly is overly complicatedand expensive. Moreover, there is no disclosure relating to locating themain fuse link so as to avoid interference with the conductor wire.

U.S. Pat. No. 4,204,182 to Knapp, Jr. discloses a fuse having a bodycontaining an arc-quenching filler. A single fuse element is connectedto a terminal at one end, and to a conductor rod at the other end. Apartition wall is provided which partially surrounds the conductive rod.A tubular member is also provided at an end of the fuse which partiallysurrounds the conductive rod. The inclusion of a granular filler adds tothe cost of the fuse and may adversely affect the operation of the fuse.The filler must be contained by a partition with a relatively largeopening, and by a mass of silicone grease. In addition, there is noseparate conductor wire to restrain the indicator pin.

U.S. Pat. No. 3,636,491 to Cameron discloses an indicating fuse thatcontains an arc-quenching filler. A plurality of fuse elements connect apair of opposing terminals. A restraining wire is attached to anindicating plunger. A housing member surrounds the indicating plunger.The restraining wire passes through a large opening in the housingmember, is connected to the indicating plunger, then exits the openingand is connected to a terminal. The inclusion of a granular filler addsto the cost of the fuse and may adversely affect the operation of thefuse. The indicator assembly appears especially prone to contaminationby the filler due to the large opening in the housing member. There isno disclosure of locating the main fuse element(s) so as to minimizepossible interference with the conductor wire.

OBJECTS AND SUMMARY

The present invention overcomes the above mentioned problems, andothers, by providing an indicating fuse construction that incorporates aprotective shield member.

One preferred form of the invention includes a fuse having a fuse bodyand terminal portions at opposite ends of the fuse body. A main fuselink is electrically connected to each of the terminal portions. Anindicator assembly is incorporated within the fuse and a conductor wireis electrically connected to one of the terminal portions and to theindicator assembly so that destruction of the electrically conductivewire activates the indicator assembly thereby indicating a blown-fusecondition. A shield member encompasses the indicator assembly. The fusecan be essentially free of filler material. In certain applications, afiller material may be used in conjunction with the shield member.

A fuse constructed according to the present invention may include a fusebody with terminal portions at opposite ends of said fuse body. Anindicator assembly is incorporated within the fuse. A conductor wire iselectrically connected to one of the terminal portions and to theindicator assembly, whereby destruction of the electrically conductivewire activates the indicator assembly thereby indicating a blown-fusecondition. A shield member encompasses the indicator assembly. A firstend of a main fuse link is electrically connected to one of the terminalportions. The main fuse link has a first angled transition sectionextending from the first end that diverges away from the conductor wirein order to prevent contact and interference between the main fuse linkand the conductor wire. The main fuse link has a second sectionextending from the angled transition area and passing between anexterior surface of the shield and an interior surface of the fuse body.The main fuse link terminates at a second end that is in contact withthe other terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the pin indicating fuse of the presentinvention.

FIG. 2 is a top view of the pin indicating fuse of FIG. 1.

FIG. 3A is a cross-sectional view of a prior art fuse design.

FIG. 3B is a cross-sectional view taken along lines 3--3 of FIG. 2.

FIG. 4 is a side view of a protective shield of the present invention.

FIG. 5 is a top view of the shield of FIG. 4.

FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 5.

FIG. 7 is a sectional view of certain components of a fuse constructedaccording to the present invention.

FIG. 8 is a partial view of FIG. 7 from a different perspective.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fuse constructed according to the present invention 10 includes adevice 12 for indicating a blown fuse condition.

The fuse 10 has an elongated body 16. While the fuse illustrated in thedrawings has a cylindrically-shaped body with a longitudinal axis A, itshould be evident that the fuse may be of any suitable shape (e.g.,rectangular, or another polygon). The fuse body 16 is constructed of anelectrically insulative material such as a glass-melamine resin materialor spiral-wound vulcanized tubing.

An orientation ring 14 may be provided about the periphery of the fusebody 16. The orientation ring 14 serves to insure proper installation ofthe fuse 10. The precise construction and function of such anorientation device is described in U.S. Pat. No. 5,594,404, thedisclosure of which is incorporated herein by reference. Alternatively,orientation ring 14 may be omitted.

Terminals 18 and 20 are provided at opposite ends of the fuse body 16.The terminals 18, 20 may be secured to the fuse body 16 by any suitablemethod, such as crimping. Any suitable terminal shape or constructionmay be employed. In a preferred form of the invention, the terminals 18,20 are of the ferrule-type. The terminals 18, 20 are constructed of anelectrically-conductive material, such as silver-plated copper,silver-nickel alloy, albaloy plated copper, copper alloy material.

An indicator assembly 44 is disposed substantially within the fuse body16. The indicator assembly is best illustrated in FIGS. 3B and 7. Theindicator assembly includes an indicator pin 46. One end of theindicator pin 46 is in the form of an enlarged flat or "planished"formation 48 having an arcuate groove 50 formed therein. An enlargedhead 54 is provided at the opposite end of the pin 46. The enlarged headportion 54 of the indicator pin 46 may be brightly colored, or providedwith other means to improve its visibility.

A bias member sleeve 56 surrounds at least a portion of the indicatorpin 46. The bias member sleeve 56 has a mounting flange 60 that restsupon a mounting ledge 62 provided on the terminal 20. The mounting ledge62 defines a central aperture which receives the bias member sleeve 56.The bias member sleeve may be received with an interference fit in thecentral aperture. The bias member sleeve 56 may be affixed to theferrule by any suitable means, such as the above-mentioned interferencefit, soldering, or both.

A biasing member 58 is provided within the biasing member sleeve 56 andsurrounds at least a portion of the indicator pin 46. The biasing member58 may be of any suitable construction. In a preferred form, the biasingmember 58 comprises a helical coil spring. In the illustratedembodiment, one end of the biasing member 58 rests on the a bottom ofthe sleeve 56, while the other end engages the enlarged head 54 of thepin 46. Due to energy stored by the biasing member 58, the indicator pinis urged outwardly from the fuse during activation of the indicatorassembly 44. It should be noted that the enlarged end 48 of theindicator pin 46 is larger than the opening formed in the bottom ofsleeve 56, thereby acting as a "stop" which prevents the indicator pin46 from being entirely ejected from the fuse.

A protective shield 34 is disposed within the fuse so as to surround theentire indicator assembly 44. The protective shield 34 is bestillustrated in FIGS. 3B and 4-6. Shield 34 can be formed of any suitablematerial, such as metal or plastic. In a preferred embodiment, theshield 34 is formed of a liquid crystal polymer. One such polymer iscommercially known as XYDAR G930™ resin.

The shield 34 has a conically shaped end 36. The precise dimensions andshape of the shield 34 can vary widely. In one preferred form theconical end defines an included obtuse angle "θ" of approximately 120°.A small passage 37 is formed in the conical end. By way of example only,the diameter of the small passage D37 can be approximately 0.46 mm(0.018 inches).

The shield 34 has a generally cylindrical section or body 38, and amounting flange 40 disposed at the end opposite from the conicallyshaped end 36. The mounting flange 40 includes a slot or passage 39disposed therein, the purpose of which will be described below. Themounting flange 40 rests upon an end of the fuse body 16.

Shield 34 can enable fuses having a rating of 5 Amps or greater tofunction properly, even in the absence of an arc-quenching filler.

A main fuse link 22 electrically connects both terminals 18, 20. Mainfuse link 22 has a first end 24 in contact with one terminal 18. Solder26 may be introduced at terminal 18 to secure the main fuse link 22 andimprove the electrical connection. The main fuse link 22 can have anangled transition area 28 extending from the first end 24. In apreferred embodiment, a "weak spot", such as an area of reduceddimensions 29 (see FIG. 7) is provided in this angled transition area28. The "weak spot" is provided as a way of designating the location ofthe fuse that will be destroyed in the event that the fuse is "blown" orsubjected to a current level above that which it is intended to carry.Preferably, the weak spot or area of reduced dimension 29 islongitudinally centered between the terminal 18 and the conical end 36of the shield 34, thereby reducing the possibility that the main fuselink 22 will interfere with activation of the indicator assembly 44.

The main fuse link 22 extends from the angled transition section 28between the exterior surface of the shield 34 and the interior surfaceof the fuse housing 16. This section 30 of the fuse link 22 can take anyform necessary. In a preferred embodiment, section 30 is generallyplanar.

The main fuse link 22 terminates at a second end 32. The second end 32passes through the slot 39 in the shield 34 and through a passage 64formed in the mounting ledge 62 of terminal 20.

In the event that the shield 34 is formed from metal, it may not benecessary to bring the main fuse link 22 into direct contact withterminal 20. For example, terminal 20 would be electrically connected toshield 34 via metallic mounting flange 40. Therefore, the second endcould be brought into contact with the shield alone to make thenecessary electrical connection.

The main fuse link 22 can be formed from any suitable conductivematerial. By way of example only, the main fuse link 22 can beconstructed of zinc. The fuse link 22 can be made from any suitablefusible material known to those of ordinary skill in the art.

A conductor wire 42 is attached at one end to a terminal 18. The wire 42can be attached to the terminal 18 by solder 26. Wire 42 passes throughthe passage 37 in the conically-shaped end 36 of the shield. Thediameter of the passage 37 is slightly larger than the diameter of thewire. For example, the wire can pass through the passage 37 with aradial clearance of approximately 0.006 inches. The wire 42 is alsoattached to at least the enlarged flat end 48 of the indicator pin 46.The wire 42 may also be wrapped around arcuate notch 50 a few turns,then continue along indicator pin 46 in a helical manner. As illustratedin FIGS. 7 and 8, the wire 42 can also extend around the exterior of thebias member sleeve and under mounting flange 60. Therefore, theconductor wire is electrically connected to both terminals 18, 20. Inthe event of a current overload, at least a portion of the wire 42between the terminal 18 and the flat end of the pin 48 is destroyed andthe pin 46 is released. The helical windings of the wire 42 can collapseupon each other as the pin 46 is ejected thereby avoiding interferencewith pin 46 as it travels through the hole in the bottom of sleeve 56.The precise manner in which the conductor wire 42 is attached to theindicator assembly can vary so long as the requisite electricalconnection between the terminals 18, 20 is achieved.

While intact, the conductor wire 42 restrains the indicator pin 46. Thewire 42 is strong enough to prevent the biasing member 58 from urgingthe indicator pin 46 outward.

In certain lower amperage rated fuses, conductor wire 42 may also serveas the main fuse link, thereby enabling omission of a separate main fuselink element 22.

This fuse construction provides several advantages. The shield 34isolates the indicator assembly 44 from the main fuse link 22 and helpsclose the end of the fuse from which the indicator pin 46 projects.Therefore, the electrical arcing and gases produced when the main fuselink 22 is destroyed can be adequately contained without resorting tothe use of an arc-quenching filler. Consequently, the fuse of thepresent invention 10 is less costly to manufacture and more reliable inoperation. Moreover, the location of the main fuse link 22 and itsisolation from the indicator assembly 44 by shield 34 helps preventinterference with the activation of the indicator assembly upondestruction of the main fuse link 22.

Operation of the fuse of the present invention 10 will now be described.

During normal operating conditions, current is carried through the fuse10 primarily via the main fuse link 22. During an overload situation,the main fuse link 22 is destroyed, preferably in the area of the "weakspot" or area of reduced dimensions 29. Current is then diverted to wire42. Since the capacity of wire 42 to carry current is substantially lessthan that of the main fuse link 22, conductor wire 42 is quicklydestroyed as well. At this point the wire 42 is no longer able torestrain the indicator pin 46, and the biasing member 58 is free to urgethe indicator pin outwardly away from the fuse body 16. The indicatorpin 46 is "stopped" from being totally ejected from the fuse by enlargedend 48 which cannot pass through the opening defined in the bottom ofbias member sleeve 56.

Only preferred embodiments of the invention are specifically illustratedand described herein. It should be appreciated that numerousmodifications and variations of the present invention are possible inlight of the present disclosure, such modifications and variations beingencompassed within the scope of the appended claims without departingfrom the spirit and scope of the present invention.

What is claimed is:
 1. A fuse comprising:a fuse body having alongitudinal axis; terminal portions at opposite ends of said fuse body;a main fuse link electrically connected to each of said terminalportions; an indicator assembly, maid indicator assembly comprising anindicator pin having a first and second end opposite said first end, abias member, and a bias member sleeve completely surrounding said biasmember; a conductor wire electrically connected to said terminalportions, and attached to said indicator assembly, whereby destructionof said conductor wire activates said indicator assembly therebyindicating a blown-fuse condition; an insulative shield member separatefrom said fuse body and radially encompassing said indicator assembly,said shield extending longitudinally so as to longitudinally encompasssaid indicator assembly from a point near said first end of saidindicator pin to at least a point at said second end of said indicatorpin; and said fuse is essentially free of filler material.
 2. The fuseof claim 1, wherein said fuse is rated for service at 5 Amps or more. 3.The fuse of claim 1, wherein said shield has a generally cylindricalbody and has a first conically-shaped end portion.
 4. The fuse of claim3, wherein said shield has a second end opposite from saidconically-shaped end, and a mounting flange disposed on said second endthat rests upon an end of said fuse body.
 5. The fuse of claim 1,wherein said shield is formed of a liquid crystal polymer.
 6. The fuseof claim 3, wherein said conical end has a passage formed therein, andsaid conductor wire passes through said passage with a close clearance.7. The fuse of claim 6, wherein said close clearance is no greater thanapproximately 0.006 inches.
 8. The fuse of claim 1, wherein saidconductor wire is attached to one of said terminal portions and to atleast one of said first and second ends of the indicator pin in order toretain said indicator pin substantially within said fuse body while saidfuse is in a normal operative condition.
 9. The fuse of claim 1,wherein:said indicator pin is centrally-located and has an enlarged headportion, said indicator pin being dimensioned such that at least saidenlarged head portion extends beyond the fuse body upon activation ofsaid indicator assembly; said bias member sleeve surrounding saidindicator pin and mounted to one of said terminal portions; said biasmember housed within said bias member sleeve and contacting saidenlarged head portion to urge said indicator pin outwardly away fromsaid fuse body upon activation of said indicator assembly; and saidconductor wire is attached to one of said terminal portions and to anend of said indicator pin in order to retain said indicator pinsubstantially within said fuse body when said fuse is in a normaloperative condition.
 10. The fuse of claim 9, wherein:one of saidterminal portions comprises a ferrule, said ferrule having a mountingledge disposed thereon; and said bias member sleeve includes a mountingflange that rests upon said mounting ledge.
 11. The fuse of claim 1,wherein said main fuse link is located outside of said shield.
 12. Thefuse of claim 11, wherein said main fuse link has a section of reduceddimension, said section of reduced dimension being longitudinallycentered between said conically-shaped end of said shield and one ofsaid terminal portions.
 13. The fuse of claim 1, wherein:a first end ofsaid main fuse link is soldered to one of said terminal portions; saidmain fuse link having a first angled transition section extending fromsaid first end that diverges away from said conductor wire in order toprevent contact and interference between said main fuse link and saidconductor wire; said main fuse link having a second generally planarsection extending from said angled transition area and passing betweenan exterior surface of said shield and an interior surface of said fusebody; and said main fuse link extending through a slot formed in saidshield and terminating at a second end that is in contact with the otherof said terminal portions.
 14. The fuse of claim 1, wherein said fuseincludes an orientation ring attached to the outer periphery of saidfuse body.
 15. The fuse of claim 1, wherein said terminal portions areferrules constructed from a material chosen from the group consistingof: silver-nickel alloy, albaloy-plated copper, copper alloy, andsilver-plated copper.
 16. The fuse of claim 1, wherein said conductorwire serves as said main fuse link.
 17. A fuse comprising:a fuse bodyhaving a longitudinal axis; terminal portions at opposite ends of saidfuse body; an indicator assembly, said indicator assembly comprising anindicator pin having a first end an a second end opposite said firstend, a bias member, and a bias member sleeve completely surrounding saidbias member; a conductor wire electrically connected to said terminalportions, and attached to said indicator assembly, whereby destructionof said conductor wire activates said indicator assembly therebyindicating a blown-fuse condition; an insulative shield member separatefrom said fuse body and radially encompassing said indicator assembly,said shield extending longitudinally so as to longitudinally encompasssaid indicator assembly from a point near said first end of saidindicator pin to at least a point at said second end of said indicatorpin; and a main fuse link, a first end of said main fuse link iselectrically connected to one of said terminal portions, said main fuselink having a first angled transition section extending from said firstend that diverges away from said conductor wire in order to preventcontact and interference between said main fuse link and said conductorwire, said main fuse link having a second section extending from saidangled transition area and passing between an exterior surface of saidshield and an interior surface of said fuse body, and said main fuselink terminating at a second end that is electrically connected with theother of said terminal portions.
 18. The fuse of claim 17, wherein saidmain fuse link has a section of reduced dimension, said section ofreduced dimension being longitudinally centered between saidconically-shaped end of said shield and one of said terminal portions.19. The fuse of claim 17, wherein said shield has a generallycylindrical body and has a first conically-shaped end portion.
 20. Thefuse of claim 19, wherein said conical end has a passage formed therein,and said conductor wire passes through said passage with a closeclearance.
 21. The fuse of claim 19, wherein said shield has a secondend opposite from said conically-shaped end with a mounting flangedisposed on said second end that rests upon an end of said fuse body, aslot is formed in said second end of said shield, and said second end ofmain fuse link extending through said slot formed in said shield andcontacts the other of said terminal portions.